The invention relates to a measuring, monitoring and regulation system for determining the locking pressure, column force and/or casting force in pressure diecasting machines. In the zone of the column nut the system has a measuring device which detects the values to be measured and applies signals to a regulating device for adjusting the locking force, if required.
From the publication: Ernst Brunnhuber "Praxis der Druckgussfertigung" (Pressure Die casting Production Practice), 3rd Edition, 1980, the basic construction of pressure diecasting machines is known (pages 28 et seq.). Pressure diecasting machines accordingly consist essentially of two main groups of components, namely the die closing unit and the casting unit. Other groups of components comprise the ejector unit, the core puller, and the machine drive including its control means.
The die closing unit serves to open and close the die, that is to say to move the one movable half of the die and to produce the locking force during the casting. The fixed clamping plate here serves to receive the stationary half of the die and, in cold-chamber machines, also to receive the casting equipment comprising the casting chamber and casting plunger. The movable clamping plate receives the movable half of the die. The movable clamping plate is usually guided on four longitudinal columns or guide columns, the latter serving to receive the locking force generated by the die closing unit and also to guide the movable clamping plate.
The die closing unit may be driven by a hydraulic closing cylinder (purely nonpositive locking) or by a known double toggle lever system with a hydraulic closing cylinder as drive means for positive locking. The locking force must be sufficient to overcome the counter-forces occurring during casting. The die is accordingly subjected to prestressing which overcomes the casting forces. All positive locking systems require extremely accurate adjustment of the die height, that is to say the overall height of the entire pressure diecasting die parallel to the closing axis, in order to generate the required locking force when the die is closed. The entire closing mechanism must therefore be longitudinally adjustable, this being achieved in modern machines by means of electric motor-driven die height adjustment acting uniformly on all four columns. The rear column nuts, for example, serve in this case as adjusting nuts, which for example are operated by a geared motor by way of gearing.
The locking force generated in a toggle lever arrangement depends on the extended position of the toggle lever at a given moment and must not in any circumstances go beyond the top dead center position. The locking force achieved must therefore be determined very accurately. In known pressure diecasting machines this is achieved with the aid of known measuring and monitoring systems determining and monitoring the locking force. In practice the locking force is measured by means of the column expansion occurring in such arrangements. This can, for example, be done with the aid of a dial gauge installed at the end of the guide column and pressing by means of its feeler pin against a rod which is inserted into the bored column and does not participate in the expansion of the column. The amount of the expansion between the column nut and the fastening of the rod can thus be read on the dial gauge. This solution has the disadvantage that deep-hole drilling is required in the columns and thus electric lines must be connected and disconnected for the pulling or dismantling of the columns.
Another known possible way of detecting column expansion consists in fastening wire strain gauges on the guide columns. In addition, there are electronic monitoring devices which detect the column expansion or, in toggle lever closing units, the hydraulic pressure required in the closing cylinder for the extension of the joints.
The force on the columns of a pressure diecasting machine in continuous operation can also be detected by means of rings disposed under the column nuts and fitted with appropriate wire strain gauges. However, this solution has the disadvantage of being very expensive to construct and of being difficult to install and to remove.
Measuring and monitoring systems for the evaluation of the column force are also known, which compare the measured values with optimum values. In the event of a noteworthy divergence of the measured value, the stress in the columns is readjusted to the optimum values by automatic correction of the die height adjustment. Automatic regulation of the locking force can in this case be achieved by measuring the peak value of the closing pressure on the extension of a double toggle lever system in the closing unit, the measured value being brought in the regulation device into relationship with the actual locking force, displayed digitally and, if necessary, automatically corrected by stepping adjustment.
All known systems for measuring or monitoring the locking force in a pressure diecasting machine are relatively complicated in construction.
It is an object of the invention to provide a simplified measuring and monitoring system which meets the requirements existing at the present time and with which in addition the range of application is widened.
This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the diecasting machine includes a transverse member; a column passing through the transverse member; and a column nut mounted on the column and having an underface being in a face-to-face engagement with a surface area of the transverse member. The column nut applies, with its underface, pressure forces on the surface area of the transverse member. Such pressure forces are derived from forces generated in the diecasting machine, taken up by the column and transmitted by the column to the column nut. The transverse member has a measuring bore which is situated adjacent the surface area of the transverse member and which has an axis oriented transversely to the length dimension of the column. A measuring plug is accommodated in the measuring bore for detecting the pressure forces applied to the surface area by the underface of the column nut and for emitting signals representing magnitudes of the pressure forces. A regulating device receives the signals from the measuring plug for regulating diecasting operations of the diecasting machine as a function of the signals.
The measuring, monitoring and regulation system according to the invention has the advantage over known arrangements that it has a very simple and effective construction. The system according to the invention then also makes it possible for variations, for example those caused by the action of temperature, to be corrected by appropriate regulation pulses. This system is based on the abandonment of direct measurement and evaluation of column expansion. On the contrary, pressure stresses which are proportional to the column force and thus to column expansion are detected by a pressure sensor. According to the invention the pressure sensor required is disposed in the region of the maximum pressure stresses acting on the casting machine. Heavy pressure stresses in the machine casing occur in particular in the region of the column nuts dictating the locking force.
Moreover, in addition to the measurement of the column force in continuous operation and therefore the determination of the locking force of the dies, the invention also provides for the casting force itself during continuous operation to be determined and evaluated. The casting force can thus be determined in accordance with the invention by setting the locking force to a fixed value or to zero before the die filling operation and by determining and evaluating the casting pressure in the die during the actual casting process as a casting force over and above said value.
According to the invention a corresponding measuring device is disposed in the region of the rear column nuts, which are in the form of adjusting nuts. Additionally or alternatively, the measuring device may also be provided in the front, fixed clamping plate for the die in the region of the column nuts provided there.
Finally, the invention provides for a corresponding measuring device for determining the casting force to be disposed on the casting equipment holder, and in particular on the casting part cross member situated there, near the support rod nuts.